Numerous proposals have been made heretofore to provide a solar hot water system; however, inherent in such a system is the problem of providing efficient heating of the water in a hot water tank of the system and maintaining the water heated with minimum heat loss. Another problem encountered with a solar hot water system is the necessity of assuring that, in the event of failure of system components, a heat transfer liquid normally employed in the energy transport subsystem of the overall system does not contaminate the cold water supply.